
On-device translation used to mean a separate model for every language you wanted to support. English to French, English to German, and so on. However, that becomes unsustainable at a global scale when you’re talking about thousands of possible language pairs.
Add to that the fact that most developers have to either send translation requests to the cloud to get fast, accurate results, or keep it local with restricted language support.
Tether’s AI Research team has developed a family of multilingual translation models, TranslatePsy-EuroNano, that each support nine European languages, with deployment built around a pair of multilingual models rather than separate bilingual models for every language pair.
What makes this possible
Supporting a full European market on-device has previously meant bundling dozens of separate model files, but this is impractical for mobile apps and those building them.
Tether AI’s multilingual open‑source edge translation models set the standard for efficiency, quality, and speed. For developers, the possibilities are endless.
Using English as a pivot, the models remain comparable to Mozilla Firefox’s Bergamot-based translation system while dramatically reducing the size of on-device translation.
At its smallest tier, Tether’s deployment is 17.6 times smaller while maintaining comparable translation quality.
Tether’s deployment takes up 36MB to 89MB, depending on the tier you use. By comparison, the equivalent Firefox setup requires 18 separate bilingual models totaling 633MB to provide the same language coverage.
The models are small enough to run efficiently on edge devices while supporting nine European languages from a single multilingual deployment, making multilingual experiences practical for a much wider range of software.
Potential applications include travel and navigation apps, educational platforms that present lessons and resources on-device. The models are also designed for academics and researchers.
Because the weights are openly available, researchers can fine-tune them for specialized domains, like customer support chatbots, virtual assistants, educational tutors, and question-answering systems, then publish those improved models for others to build on. Rather than a single translation application, the models become a foundation for multilingual AI systems.
No third party involvement
Think about the last time you used your phone abroad. Perhaps you used a translation app, typed something in, and a couple of seconds later, the translation appeared. What you probably didn’t think about is where your text went in that half-second.
Before a translation appears on your screen, the data goes through a journey that crosses a number of middlemen. Your data leaves your phone through an encrypted data packet, is routed to a regional server, and then goes to a data center. That is, unless you are using offline translation.
When translation runs entirely on-device, text never leaves the user’s device. There are no intermediary servers, no additional data-processing agreements, no cross-border data transfers, and greater clarity over how user data is handled.
How Tether’s models work
Instead of training a separate model for every language pair, Tether trains a single multilingual model capable of translating between English and nine European languages.
Using English as a pivot, two multilingual models enable translation across all ten languages (English plus nine European languages), providing 90 possible translation directions, including English to European, European to English, and European to European translation.
Unlike approaches that fine-tune existing pretrained translation checkpoints, Tether trained these models from scratch using independently curated and preprocessed open-source parallel data. No pretrained model checkpoint was used for initialization.
The compression ranges from 7 to 17.6 times smaller than the previous on-device approach for equivalent coverage, depending on the tier. The advantages are seen across storage, speed, and how closely the quality compares to much larger systems.
Firefox’s Bergamot-based translator needs a separate bilingual model for each language direction. Covering nine European languages both ways means loading 18 models, a 633MB bundle on disk.
Tether’s approach uses two multilingual checkpoints per tier, one for each direction, covering all nine languages with a single load. Loading fewer, smaller models also means faster responses. In controlled CPU benchmarking on the FLORES-200, Firefox took 10.8 seconds to return its first translated sentence. TinyQ returned it in 4.2 seconds, over twice as fast, and BaseQ in 6.8 seconds.
BaseQ, the top tier, retains 98.4% of NLLB-200’s translation quality, translating into English, and closely tracks Firefox’s own score despite using a fraction of the storage. The gap widens a little when translating out of English, which is typical for a multilingual model sharing one decoder across languages rather than using a dedicated model per language pair.
Other translation models
Tether’s European models aim to be the most efficient, highest-quality, fastest open-source multilingual translation model built for the edge. Alongside its European language models, Tether AI Research has also released a set of models for African languages, TranslatePsy-AfriSLM, in response to AI underinvestment on the African continent that has created a significant barrier to adoption for over a billion people.
Tether’s TranslatePsy-AfriSLM is a collection of open-source machine translation resources covering 19 Sub-Saharan African languages. These models outperform much bigger models such as TranslateGemma (by Google) and NLLB (by Meta).
Existing open-source LLMs underperform on African machine translation, and the shortage of large-scale, high-quality, open-source parallel data has constrained the development of competitive small language models in this space.
Making language models accessible on-device while maintaining efficiency, quality, and speed has been a challenge up until now. Keeping AI local, and making sure that everybody can access it is a fundamental part of Tether’s mission.
The European translation models and TranslatePsy-AfriSLM are available now through QVAC SDK for integration across Android, iOS, Linux, macOS, and Windows.
Check out the QVAC repo now.





















